The principal aim of this investigation is to understand the basic mechanisms operating in chemoreceptors. Two main goals have been set and experiments are in progress in their analysis: 1) the role of the nerve are being investigated by the development of a sucrose gap in order to record from these structures as closely as possible; 2) intracellular studies of glomus (type I) cells are being conducted, the cell constants measured and the effects of a number of agents are under investigation. It has been found that the nerve endings are quite sensitive to the composition of the medium being hyperpolarized in low K ion and depolarized in an excess of this ion. Also, lack of sodium induces ending hyperpolarization. Lack of Ca2 ion induces ending depolarization and an excess of this ion has the opposite effect. The effects induced by lack of calcium are only partially compensated by an excess of magnesium ions. The glomus cells are markedly depolarized with a loss of input resistance if the temperature of the bathing solution is allowed to fall. Cells are hyperpolarized in alkaline (pH 8.5) solutions and depolarized in acid (pH 6.5) saline. CO2 has no clear effects if the pH of the bathing medium is held constant. Other stimulating agents such as ACh, NaCN and N2 while markedly increasing the sensory discharges do not change the input resistance and membrane potential of the cells. Lack of flow (a powerful stimulus of the chemoreceptors in vitro) induces clear cell depolarization and a marked loss of input resistance. Work is continuing in order to learn more about the relationships between glomus cell activity and nerve discharges. BIBLIOGRAPHIC REFERENCES: Gallego, R. and C. Eyzaguirre (1976). Effects of osmotic pressure changes on the carotid body of the cat in vitro. Fed. Proc., 35:404. Zapata, P., L.J. Stensaas and C. Eyzaguirre (1976). Axon regeneration following a lesion of the carotid nerve: Electrophysiological and ultrastructural observations. Brain Res. 113:235-252.